1. Field of the Invention
The present invention generally relates to an inductor structure, and more particularly, to an inductor having a three-dimensional helix structure.
2. Description of Related Art
In general, an inductor functions as a device for saving and releasing energy through the inter-conversion between electrical and magnetic fields. Therefore, an inductor can serve as a current-stabilizing device. In integrated circuits, inductors are important but challenging passive devices. In addition, the range of application of the inductors is very wide. For example, inductors are often used in radio frequency circuits. The performance of an inductor is based on its quality factor represented by a Q value. The higher the Q value of the inductor, the better the quality of the inductor is. The Q value is defined by the following formula: Q=ω×L/R, wherein, ω is the angular frequency, L is the inductance of the winding, and R is the resistance when the inductor loss is considered within a designated frequency range. According to the above formula, the Q value is inversely proportional to the resistance. In other words, the Q value will increase by lowering of the resistance. Yet, the resistance is directly proportional to the square of the current density. Therefore, a method of increasing the Q value is to increase the section area of the metal winding so as to reduce the resistance. In other words, the resistance of the metal winding is reduced to minimize conductor loss and achieve the goal of increasing the Q value.
At present, a number of methods and techniques have been developed to integrate the process of fabricating inductors and integrated circuits. However, in an integrated circuit, the limitation of inductor metal thickness and the interference of the inductor by the silicon substrate will lead to a lower quality inductor. The conventional technique of disposing a thicker metal on the uppermost inductor structure to increase the section area of the inductor metal and lower the conductor loss is used to increase the Q value of the inductor. However, when the thickness of the metal is increased up to a certain level, the improvements in conductor loss and Q value become less prominent. Therefore, how to resolve the foregoing problems, increase the Q value and reduce the conductor loss is high on the developing list.